Electrodeposition of copper



3,414,493 ELECTRODEPOSITION OF COPPER Fred I. Nobel and Barnet D.Ostrow, Roslyn, N.Y. (both Ii/ i lgea-Ronal Inc., 13019 180th St.,Jamaica, N.Y.

4 4 No Drawing. Filed Oct. 19, 1965, Ser. No. 498,084 8 Claims. (Cl.204-52) This invention relates to electroplating and more particularlyto electrodepositing copper from an aqueous acidic copper plating bathin which there is dissolved a small amount of a brightening agent.According to this invention, the brightening agent is an organicsulfonic acid or its water soluble salts having the general structuralformula:

wherein R is H or an alklene radical having 1 to 3 carbon atoms, m and nare integers of which in is at least 1 and n is from 3 to 8, and G is anitrogen-carbon-sulfur radical having the general structural formula:

in which R is an aromatic radical or its alkyl derivative, and R and Rare alkyl radicals. R and the combination of R and R may also be cyclicalkyl radicals linking to the single bonds of S and N in (a) for R andthe double bond of N in (b) for the combination of R R A preferredbrightener would have the following structural formula in which R and Rare as defined above and M is H Na or K.

It is understood that in subsequent descriptions in the preparation ofthe brightener H, Na and K are interchangeable depending on the startingmaterial,

Preferably, the brightening agents of this invention are prepared byinitially reacting a nitrogen-carbon-s-ulfur organic compound with analkyl aldehyde in an alkaline solution and subsequently adding a sultoneto the reaction mixture to produce the brightening agent of thisinvention.

The nitrogen-carbon-sulfur organic compounds suitable for the presentinvention all contain an organic radical which comprises a carbon atombonded exclusively to hetero atoms, nitrogen, and sulfur. In otherWords, the compounds contain the radical having the general structuralformula:

Linked to one of the S and the N in (c) may be an aromatic or a cyclicalkyl radical and to the N in (d) may be alkyl radicals or a cyclicalkyl radical. The second S is connected to a H, an alkyl or othernitrogensulfur radicals. Typical compounds of this type suitable for thepresent invention include:

(I) l,3-bis(2-benzothiazolylmercaptomethyl)urea (II)N-cyclohexyl-Z-benzothiazolesulfenamide (III)2,2'-,dithiobis(benzothiazole) (IV) Z-mercaptobenzothiazole C-SH (V)Piperidium-l-piperidinecarbodithioate CHz-CH: GHQ-CHI H20 N 0 CH1 (VI)N,N-dimethylcycloamine salt of dibutyldithiocarbamic acid Hack H\(,JH3CH:|-CH2 NC-sN-0H 011,

(VII) Bis (diethylthiocarbamyl disulfide (IX) Bis(dimethylthiocarbamyl)disulfide Among these compounds, we found Compounds IV, VII,

VIII, and IX to be eminently suitable and are the preferred startingmaterials.

The alkyl aldehyde used in the reaction is preferably a lower alkylaldehyde containing not more than 3 carbon atoms. In reactions using thepreferred nitrogen-carbonsulfur organic compounds stated above, we foundparaformaldehyde to be particularly suitable.

In the first stage of the reaction, the N-C-S organic compound ispreferably dissolved in an alcoholic or an aqueous solution, or analcohol-water mixture together with an equal molar amount of an alkalimetal hydroxide, preferably sodium hydroxide, to form the N-C'=S alkalimetal salt in solution. Added to the reaction solution is one or moremols of aldehyde for each mol of N-CS organic compound and the reactionmixture is refluxed for a period of time depending on the reactantsused. Generally, one-half hour is sufiicient to insure completereaction. The resultant solution is used in the third stage of thereaction in which sultone is added therein. In the later stage, thereaction is also preferably carried out in the reflux temperature untilcompletion.

The sultones used in the second stage have in general the structure:

wherein R" and R' are hydrogen atoms or alkyl radicals, and R is analkylene radical of up to 2 carbon atoms, preferably l,l-alkylene.Sultones that are particularly suitable are those in which R ismethylene or R-substitutecl methylene, and each R is hydrogen or alkylof up to 4 carbon atoms. The total number of carbon atoms is preferablyfrom 3 to 8. Typical sultones that are found to be suitable include:l-propane sulfonic acid 3-hydroxysultone; l-butane sulfonic acid4-hydroxysultone; l-butane sulfonic acid 3-hydroxysultone; 2-butanesulfonic acid 4- hydroxysultone; 2-pentane sulfonic acid4-hydroxysultone; l-pentane sulfonic acid S-hydroxysultone; 2-methyl-2-pentane sulfonic acid 4-hydroxy-sultone; 4-heptane sulfonic acid6-hydroxysultone; l-heptane sulfonic acid 3- hydroxysultone; l-heptanesulfonic acid 4-hydroxysultone; 6-methyl-l-heptane sulfonic acid3-hydroxy-sultone; 3- methyl-4-heptane sulfonic acid 2-hydroxysultone.

We found the reaction product of the reaction described above to beparticularly suitable as a brightening agent in an acid copper platingbath for electrodepositing copper. The process for producing bright andsmooth copper depOSitS comprises electrodepositing copper from anaqueous acidic solution of at least one copper salt in which there isdissolved a water soluble brightener having the structural formula:

The symbols G, R, m, n, and M have the same meaning as definedpreviously.

Only a relatively small quantity of this organic sulfonic acid or itswater soluble salt is required for the plating bath. We foundconcentrations as low as 0.005 gram per liter to be effective. Thereappears to be no sharp upper limit on the concentration of this organicsulfonic acid; however, there is generally no advantage in employingmore than 1 gram per liter. In most plating baths, substantially thefull benefit of the brightening agent is achieved with an amount in therange from 0.005 to about 0.05 gram per liter. Advantageously, theorganic sulfonic acid or its water soluble salt of this invention isisolated from the reaction solution by precipitation or crystallizationand subsequently is dissolved in water to form the additive solution tobe added directly into the plating bath.

In the process of this invention, a full brightening elfect is realizedwhen the brightening agent of this invention is used in combination wthan ethylene oxide compound. Suitable ethylene oxide compounds have thegeneral structural formula:

in which R is an aryl or alkyl containing 6 to 20 carbon atoms and n isan integer between 2 to 100. This type of compound is commonly used as anonionic wetting agent which is produced by treating fatty alcohol oralkyl substituted phenols with excess ethylene oxides. The commercialavailable agents that we found to be eminently suitable are the typeproduced by reacting oleyl alcohol or stearyl alcohol with 6 or moremols of ethylene oxide, preferably 10 or more.

Other types of ethylene oxide compound under the general classificationof amine, alkanol amine, amide and carbowax, and others containingsulfur and phosphorous heteroatoms, each of which contains a hydrophilicgroup and a large number of ethylene oxide groups, are also suitable.The ethylene oxide compounds have the following general formulas:

in which R is an alkyl or an aryl radical containing 6 to 20 carbonatoms and R is a (CH group wherein y is an integer from 1 to 6 and n isan integer from 2 to 100.

The amount required in the plating bath varies with the bath. Ingeneral, at least about 0.001 gram per liter of bath is used to securethe full brightness. An amount much more than 1 gram per liter appearsto contribute no further beneficial result.

Most commercial leveling agents may also be incorporated into theplating bath without interfering with the brightening agent of thisinvention. However, we prefer to use the leveling agent disclosed in ourcopending patent application Ser. No. 469,323 filed on July 2, 1965. Theleveling agents disclosed in that application are heterocyclicsulfur-nitrogen organic compounds, 2-thiazolidenethiones,Z-imidazolidinethiones and their reaction products with alkyl, aldehydesor dialdehydes.

Further to describe this invention specific examples are usedhereinbelow to illustrate the preparation of the specific brighteningagents of this invention and their use in an acid copper plating bathfor electrodepositing copper.

EXAMPLE I Suflicient methyl alcohol is used to dissolve one mol of 2mercaptobenzothiazole and one mol of sodium hydroxide. Into thisalcoholic solution is added one mol of paraformaldehyde and theresultant reaction solution is refluxed for one-half hour. After thefirst stage reaction, 1 mol of propane sultone is added into thereaction mixture and is refluxed for an additional one-half hour. Oneseries of reaction which can occur is illustrated by the followingequations:

C-S-OHzONa onto s \g/ recovered is a light yellow powder.

0.04 gm. per liter of this compound is added intoan acid copper platingbath which has the following composition:

G/l. Copper sulfate (CuSO -H O) 240 Concentrated sulfuric acid 60 Abrass sheet is plated at l-5 amp/dm. at 70 F. for 30 minutes. A lustrousto semilustrous coating is obtained over the current range.

EXAMPLE II 0.004 gm./liter of triethanolamine-ethylene oxide adducthaving 30 mols of ethylene oxide is added to the bath described above.The resultant copper deposits are bright over the entire current densityrange and are apparently brighter than the copper deposits of Example I.

EXAMPLE III 1 rnol of bis (dimethylthiocarbamyl)disulfide and 2 mols ofNaOH are added into a sufficient amount of methyl alcohol. To thissolution is added 2 mols of formaldehyde and the resultant solution isrefluxed for about onehalf hour before the addition of propane sultone.After the sultone addition, the reaction is carried to completion. Theresultant product has a structural formula:

0.03 gm./liter of this organic sulfonic acid salt and 0.004 gm./liter oftriethanolamine-ethyleneoxide adduct having 30 mols of ethylene oxideare added into a standard acid copper plating bath as stated in ExampleI. A brass sheet is plated at 1-10 amp/din. at 70 F. for 30 minutes.very bright copper deposits are observed over the entire currentdensity.

EXAMPLE IV Bis(diethylthiocarbamyl)disulfide instead ofbis(dimethylthiocarbamyl)disulfide is used as the starting material toprepare an organic sulfonic acid salt having the structure:

We claim:

1. A process for producing bright and smooth copper deposits whichcomprises electrodepositing copper from an aqueous acidic solution of atleast one copper salt in which there is dissolved a water solublebrightener having the structural formula:

wherein R is a hydrogen or an alkylene radical having 1 to 3 carbonatoms, m and n are integers of which m is at least 1 and n is from 3 to8, M is H, Na or K, and G is a corbon-nitrogen-sulfur radical having thestructural formula:

in which R is anaromatic radical or its alkyl derivative, and R and Rare alkyl radicals, in an amount suificient to provide a brighteningeffect.

2. A process for producing bright and smooth copper deposits whichcomprises electrodepositing copper from an aqueous acidic solution of atleast one copper salt in which there is dissolved more than about 0.005g./liter of a brightener having the structural formula:

wherein R is a hydrogen or an alkylene radical having 1 to 3 carbonatoms, In and n are integers of. which in is at least 1 and n is from 3to 8, M is H, Na or K, and G is a carbon-nitrogen-sulfur radical havingthe structural formula:

in which R is an aromatic radical or its alkyl derivative, and R and Rare alkyl radicals.

3. A process for producing bright and smooth copper deposits whichcomprises electrodepositing copper from an aqueous acidic solution of atleast one copper salt in which there is dissolved (I) more than about0.005 g./ liter of a brightener having the structural formula:

wherein R is a hydrogen or an alkylene radical having 1 to 3 carbonatoms, m and n have integers of which m is at last 1 and n is from 3 to8, M is H, Na or K, and G is a carbon-nitrogen-sulfur radical having thestructural formula:

in which R is an aromatic radical or its alkylderivative, and R and Rare alkyl radicals, and (II) more than about 0.001 g./liter of a longchain ethylene oxide compound.

4. A process according to claim 3 wherein said brightener has thestructural formula:

R2 S ll N-CSCHz-O-CHzCHzCHz-SOsM 3 in which R and R are alkyl radicalshaving 1 to 3 carbon atoms, and M is H, Na or K.

5. A process according to claim 4 wherein R and R are methyl radicals.

6. A process according to claim 4 wherein R and R are ethyl radicals.

7. A process according to claim 3 wherein said brightener has thestructural formula:

in which M is H, Na or K.

8. A process according to claim 3 wherein the said ethylene oxidecompound is water soluble and has the general formula:

in which R is an alkyl or aryl radical containing 6 to 20 carbon atoms,R is a (CH group wherein y is an integer from 1 to 6, and n is aninteger from 2 to 100.

References Cited HOWARD S. WILLIAMS, Primary Examiner.

G. KAPLAN, Assistant Examiner.

1. A PROCESS FOR PRODUCING BRIGHT AND SMOOTH COPPER DEPOSITS WHICHCOMPRISES ELECTRODEPOSITING COPPER FROM AN AQUEOUS ACIDIC SOLUTION OF ATLEAST ONE COPPER SALT IN WHICH THERE IS DISSOLVED A WATER SOLUBLEBRIGHTENER HAVING THE STRUCTURAL FORMULA: